Description and History

NPL Listing History

NPL Status: Final

Proposed Date: 10/15/84

Final Date: 06/10/86

Deleted Date: 08/21/06

The 5-acre T.H. Agriculture & Nutrition Company (THAN) site operated as a pesticide-formulating facility from 1962 until 1981. Other companies formulated pesticides on the site from 1950 to 1962. During the 1950s and 1960s, on-site landfills were used for disposal of wastes generated from site operations, including pesticides from cleaning equipment. Waste was spilled on the surface of the site and left in piles on the ground. Sampling at the site conducted by the California Department of Health Services (CDHS) detected pesticides in soil and groundwater. The site was listed on the Superfund National Priorities List in 1986. Cleanup activities at the site were completed in 2003 and included soil vapor extraction; demolition and removal of various structures; excavation and management of impacted soils; construction of a low-permeability containment cover to minimize the potential for movement of residual chemicals from Site soils to other media; implementation of access controls and land use restrictions; demonstration and maintenance of appropriate financial assurances; monitored natural attenuation of groundwater; provision of as-needed alternative drinking water supplies; and performance of ongoing operation, maintenance, and monitoring activities. Approximately 30,000 people live within 3 miles of the site, with the closest resident being 500 feet from the site. Approximately 35,000 people depend on groundwater as a source of drinking water.

Who is Involved

Investigation and Cleanup Activities

This site is being addressed in two stages: immediate actions and a long-term remedial phase focusing on cleanup of the entire site.

Initial Actions

Immediate Actions: T.H. Agriculture & Nutrition Company, under State supervision, excavated and removed 14,000 cubic yards of contaminated soil. All affected residences have been hooked up to the public water supply system to eliminate the use of domestic wells near the site and the threat of exposure from contaminated water. A soil vapor extraction system was used to reduce the level of volatile organic compounds in the area.

Site Studies

Entire Site: The potentially responsible party has characterized the soil contamination, monitored groundwater, and characterized the hydrogeology beneath the site. Extensive on-site and off-site groundwater studies have been conducted. The results of the groundwater field study were evaluated to identify cleanup remedies that could be applied at the site.

Remedy Selected

The draft Remedial Action Plan (RAP) was circulated for public review and comment from May 14, 1999 through June 12, 1999. A public meeting to discuss the draft RAP was held on May 26, 1999. The RAP was finalized on June 30, 1999. A major component of the soil remedy is the placement of a cap on the 5-acre site. The groundwater remedy includes long-term monitoring of wells and monitored natural attenuation (MNA). In addition, if it is found that MNA is not successful, a groundwater extraction system will be installed.

Remedy Design

The design for the cap was approved by the Department of Toxic Substances Control (DTSC) on June 28, 2002.

Cleanup Complete

Implementation of the soil remedy commenced on 11/21/02. The cap was constructed by 1/17/03. Hydroseeding and the installation of a fence was completed on 1/24/03. The site was delisted from the National Priorities List in 2006. A second Five Year Review, conducted in 2013, concluded that the cleanup is protective of human health and the environment.

Cleanup Results to Date

Cleanup activities at the site began in 1981 and were completed in 2003 and included soil vapor extraction; demolition and removal of various structures; excavation and management of impacted soils; construction of a low-permeability containment cover to minimize the potential for movement of residual chemicals from Site soils to other media; implementation of access controls and land use restrictions; demonstration and maintenance of appropriate financial assurances; monitored natural attenuation of groundwater; provision of as-needed alternative drinking water supplies; and performance of ongoing operation, maintenance, and monitoring activities. The remedy for the site has been implemented, and the site was delisted in 2006.